Cardiac Glycosides

These have a positive inotropic effect and reduce the size of a failing dilated heart leading to increased cardiac output and increased efficiency. They increase myocardial excit-ability and automaticity, depress conducting tissue and increase vagal activity. Digoxin’s half-life is more than 24 hours. The therapeutic blood level is 0.8 to 2.0mg/ml.

General Indications

(Digoxin)

Cardiac failure, atrial fibrillation, atrial flutter, paroxysmal atrial tachcardia.

Cautions/Side Effects

(Digoxin)

These usually occur at toxic serum levels above 2.0 mg/ml, but may do so in the therapeutic range especially in the elderly. Fatigue, anorexia,

nausea, visual disturbances, muscle weakness, psychic symptoms, abdominal pain, dizziness, vomiting, cardiacdisturbance - heart block,cardiac arrhythmias. Tocicity most likely with hypokalemia. Treat digoxin - induced heart block with atropine; PVC’s and ventricular tachycardia with i.v. phenytoin. These drugs must be used with caution:

(1) following acute myocar-dial infarction;

(2) within 14 days of previous treatment with cardiac glycosides;

(3) in the presence of Quinidine treatment;

(4) in the presence of severe potassium imbalance;

(5) in renal insufficiency and in the elderly (most of whom have some renal impairment).